The Development of a Complex Supraglacial Moraine at the Margin of Sørbreen, Ny Friesland, Vestspitsbergen

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Abstract
A series of concentric debris bands crop out on the frontal stagnant zone of Sørbreen, Ny Friesland, Vestspitsbergen. The contained debris, which is dominantly sand and silt with some clay and gravel, is well sorted and banded, and it is thought to be derived from subglacial fluvial deposits. These debris bands give rise to a complex series of bedded moraine ridges, and bedded and unbedded sediment sheets on the glacier surface. The development of a supraglacial hummocky moraine is traced and it is composed of several elements: supraglacial ridges, kettle-holes, and flowed sediment sheets, which are derived from debris bands; supra-glacial fluvial deposits and clay-silt ablation tills; and englacial fluvial deposits. It is also suggested that large areas of the outwash plain are underlain by dead glacier ice. From the present work there are several possible implications for the interpretation of Pleistocene deposits: i. Certain types of “controlled disintegration features” may have formed supraglacially from debris bands. Some bedded features hitherto interpreted as Huvioglacial in origin may be supraglacial moraines. ii. Certain types of “kame-and-kettle“moraine may be mainly supraglacial in origin. iii. Complex sequences of tills and bedded sediments may have been formed during a single glacier retreat phase rather than by multiple advance and retreat.